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Originally posted by BaldLoonie In our suburb, we have a common floorplan 3 bedroom 1800 sq ft ranch. We've installed 2, 2.5 and 3 tons of cooling on this exact same house. So which is right? Can you guys in Louisiana or California tell me? You told him his was wrong without seeing the house or knowing much about it.

The answer is all of them are right. Anybody going by sq ft doesn't know what they are doing. The 2 ton homes are well shaded. The 2.5 ton homes aren't shaded but face north-south with no east-west windows. The 3 ton homes are east-west facing with no shade. Hmmm, all the same house, same sq ft with radically different cooling needs. Guess that's why the Manual J was invented.

Do your California and Louisiana homes have the same insulation as his? Gee, you can't answer that - you don't know what he has yet you know his A/C is undersized. Well, my guess is he has R38 ceiling and R19 walls. That what they do in your area?

Ricardo, if you are staying comfy in the extreme heat we've been having in the upper Midwest, your system is NOT undersized. hilton's 5 ton would have you running dehumdifiers all over the place in the normal humid 82 we typically have because it would be short cycling something fierce.

Insulation is R15 in the walls. Most of the ceilings are R-38 except in the cathedral ceiling areas where they used R-30 batts. The house is fairly air tight. The contractor did a pretty good job sealing it up. Anything that he missed I've taken care of over the past two years. It definitely felt very refreshing coming in the house after doing three hours of yard work in the ninety-five degree heat.

bald loonie. not an installer or engineer.i'm in service. thousands of homes like this in cali. are you saying these home installers don't use manual j or using cheap insulation material.no difference if house on north or west shaded or not.i have also worked in resi additions never used manual j. boss used sqft and some duct calculations. this is also in a class given by ihaci in san diego. bottom line houses, customers have been fine.

let me see if i understand this. we size the equipment by the sq ft and thats it ? that sounds easy enough. And all this time i have been wasting my time accounting for r-values ,window sq footage, etc,etc,etc. I remember some years back i installed central air system i home that was poorly insulated then a few monthes later the customer calls and said that mold was growing on baseboard.when i went to customers home she told me that she had the house re insulated, well now the system is to big this is why i dont go sq footage alone.

BaldLoonie and Dash are both right on the money. Every home has a unique heat load. Whether the house is shaded or not makes a huge difference in sizing requirements. It's called solar gain. Sounds like your system is sized properly, and running great. Have the coils cleaned yearly and have a preventative checkup done. Just don't let some bonehead try to add gas to it unless they can find and fix that leak. Refrigerants don't just leave a system slowly, unless there is a leak.

Design temp for Chicago area is 91 degree outside with a 75 inside according to HVAC Calc. With the temps and humidity we have been running right now in the midwest a perfectly designed system may run continuous during the day time and run a couple degrees higher temp. If you are staying comfortable don't panic the weather will soon change, hope soon, back to normal temps.

Aircraft Mechanical Accessories Technician. The Air Force changed the job title to Air Craft Environmental Systems Technician. But I've decided I'll always be a Mech Acc.